Boundary Layer Thickness Estimator (Flat Plate) mechanism

Model scope

The thickness correlations are acceptable flat-plate idealizations when their assumptions and validity ranges are stated, but the specification is incomplete and overclaims functionality because wall shear is not defined. Add Rex, explicit unit handling, an explicit transition policy, an x=0 special case, and documented laminar and turbulent skin-friction correlations before release.

• The Reynolds-number formula is omitted even though local Rex is an output; it should be Rex=rho*U*x/mu=U*x/nu.
• The instrument claims to compute wall shear, but no wall-shear formula is supplied. A standard laminar local correlation is Cf,x=0.664/sqrt(Rex), with tau_w=0.5*rho*U^2*Cf,x; a turbulent correlation must also be selected and documented.
• The laminar thickness correlation delta=5*x/sqrt(Rex) is standard for a zero-pressure-gradient laminar flat plate, subject to the usual incompressible, smooth-wall assumptions.
• The turbulent thickness correlation delta=0.37*x/Rex^0.2 is a standard empirical flat-plate correlation, but its applicable range and whether it represents a fully turbulent-from-leading-edge approximation or a transition-corrected layer are not stated.
• No transition criterion is specified. A common engineering convention is laminar for Rex<5e5, transitional near Rex approximately 5e5, and turbulent only after transition; the exact transition location depends on free-stream turbulence, roughness, and disturbances.
• At x=0, Rex=0 and both formulas contain an indeterminate 0/0 form unless the limiting value delta=0 is explicitly handled.

Units and conventions

• Use SI units consistently: U in m/s, x in m, rho in kg/m^3, dynamic viscosity mu in Pa*s, and kinematic viscosity nu=mu/rho in m^2/s.
• If viscosity is supplied as nu, compute Rex=U*x/nu; if dynamic viscosity is supplied as mu, compute Rex=rho*U*x/mu.
• The coefficients 5 and 0.37 assume the conventional flat-plate boundary-layer definitions and zero pressure gradient.
• The supplied fluid-property table must identify whether viscosity is dynamic or kinematic; treating one as the other causes a units error.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "U_m_per_s": 15,
    "x_m": 0.2,
    "rho_kg_per_m3": 1.2,
    "mu_Pa_s": 0.000018,
    "correlation": "laminar",
    "sampled_plot_point_x_m": 0.2
  },
  "expected_outputs": {
    "Re_x": 200000,
    "flow_regime": "laminar under the stated provisional criterion Re_x<500000",
    "delta_m": 0.00223606798,
    "sampled_plot_point": {
      "x_m": 0.2,
      "delta_m": 0.00223606798
    },
    "curve_features": {
      "root": "x=0 in the limiting sense, delta approaches 0",
      "finite_extrema": "none for either supplied correlation over x>0",
      "large_x_behavior": "delta increases monotonically as x^0.5 for laminar and x^0.8 for turbulent"
    }
  },
  "working": "Re_x=rho*U*x/mu=(1.2*15*0.2)/0.000018=3.6/0.000018=200000. sqrt(Re_x)=sqrt(200000)=447.2135955. delta=5*x/sqrt(Re_x)=5*0.2/447.2135955=1/447.2135955=0.00223606798 m."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The specification does not define the transition Reynolds number or equality convention, and it does not state whether velocity is signed or converted to speed. Zero viscosity produces undefined Reynolds number and must be rejected; without explicit validation, the arithmetic engine can return Infinity, NaN, or invalid plotted values.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche6/tranche6-results.json
• BOUNDARY_HAZARD_CATALOG.json